Manufacture of molds.



C. G. ROBINSON.

MANUFACTURE OF MOLDS. APPLICATION-FILED DEC.4. 1912.

11,191,473. Patented July18, 1916.

3 SHEETS-SHEET 1- WITNESSES INVENTOR- M iA/hwy K WM v I; I.

v c. e. ROBINSON. MANUFACTURE OF MOLDS.

APPLICATION FILED DEC.4. I912.

Patented July 16, m0.

3 SHEETS-SHEET 2.

64AM Q INVEITITOR WITNESSES C. G. ROBINSON.

MANUFACTURE OF MOLDS APPLICATION. FILED DEC.4. 19-12.

Patented July 18, 1916.

FiSIQEETS-SHEET 3.

wrrmzsszs IVNVENITOR oHARLEs G. RoBINsoN, or PITTSBURGH, PENNSYLVANIA, AssIGNoR T0 HARRY n. SHELDON, or PITTSBURGH, PENNSYLVANIA.

MANUFACTURE OF MOLDS.

Specification of Letters Patent.

Patented July 18, 1916.

Application filed December 4, 1912. Serial No. 734,844.

To all whom it may concern:

Be it known that I, CHARLES G. ROBIN- soN, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented new and useful Improvements in the Mannfacture of Molds, of which the following is a specification.

The method heretofore employed in making a steel ingot-mold is as follows: A drag is first rammed with sand, and a pattern of the ingot-mold to be made is set on the drag. The pattern has the dimensions and shape of the outside of the ingot-mold. Then a cheek, having a height equal to that of the pattern, is placed over the pattern and rammed with sand. The next operation is the placing of a cope on the cheek and ramming the same with sand, space being allowed for sufficient sink-heads to properly feed the casting to be made. The copeis then lifted off from the cheek and finished. The cheek is lifted off from the drag and the pattern withdrawn therefrom. The cheek and the'drag are afterward finished. The drag, the cheek, and the cope are then placed in a drying oven and dried. After the drying has been finished, the drag is placed on the floor; then a core which has been previously made and dried, and which represents the interior dimensions of the mold to be cast, is placed on the drag; then the cheek is closed over this drag; then the cope, the drag, and the cheek are bolted together, whereupon the mold is ready to pour.

The method just outlined has several objections which it is the object of this invention to obviate. By this method the steel for the ingot mold is poured between a sand core and a sand mold. The heat of the' molten metal finds practically no escape except through the sand of the mold. Since sand is a very poor conductor of heat, the temperature of the poured metal is maintained for such a long time that the sand in the core becomes combined with the steel of the ingot mold, making the interior of the ingot mold rough and unsuitable for the casting of ingots therein. It is one of the objects of the present invention to provide an ingot mold whose inner surface shall be smooth and uncomblned with the material of which the core is composed.

Another object of this invention is to dispense with the sink-heads above mentioned and to build the cores without the usual nailing.

Another object of this invention is to make steel ingot molds so cheaply that the initial cost compares favorably with that of iron ingot molds, and to provide steel ingot molds that maintain their shape in use.

Other objects of my invention will be hereinafter set forth.

In order to secure a smooth interior of the ingot mold it is necessary to make a core. of such a composition as to withstand the initial shock of the metal during the pouring operation. I have used a core made from coarse silica sand containing between 93 per cent. and 97 per cent. of pure silica bonded together with 7 to 3 per cent. of clay. Good results may be obtained if the clay is what is known as Welsh Mountain clay and even better results may be obtained with German clay. The core not only must be strong but it must be capable of yielding to the pressure caused by the rapidly contracting steel in the mold in order that the ingot mold may not check or crack. To provide such a core I ram the same around a perforated center pipe or mandrel from 3 inches to 6 inches in diameter, according to the size of the core to be made.

After the core has been rammed and the core box in which it has been made has been removed, it is washed with a solution composed of 18 parts of ground or powdered silica, 6 parts of graphite, 1 part of salt, and 25 parts of a 50 per cent; solution of foundry molasses. This wash is applied to the outer surface of the core with a brush and slicked with a trowel.

I obtain good results by coating the core- 'plied substantially in the same manner as the other washes herein described. By the use of any of. these washes, I obtain on the core a very smooth exterior which does not require surface nailing and which is very refractory.

The pipe in the core is used both as a support for the core and as a means for facilitating the drying thereof, the core resting on a base-plate having an opening in line with the pipe.

After the core has been manufactured, an outer mold or chill, preferably composed of steel, is lowered over it, the dimensions of the mold or chill being such that the space between the same and the core conforms in size and shape to the ingot mold to be cast therein. A gas burner is applied to the bottom of the pipe opening so as to provide a current of hot air which ascends through the pipe in the center of the core, thereby causing the moisture in the core to be dried from the center outwardly, the evaporation taking place in the said space between the core and the mold.

After the core has been thoroughly dried the molten metal for the steel ingot-mold to be cast is poured from a ladle so as to occupy the said space between the core and the mold. The metal is poured through a gate and a runner so that the same enters the said molding space from the bottom. As soon as the mold has been poured, that is, within a period of ten minutes thereafter, the said center pipe in the core is withdrawn causing the core to collapse immediately, freeing the casting from any strain as it contracts In order to obtain steel ingot molds without sink-heads, I rapidly cool the metal and thereby cause the shrinkage to be absorbed.

To rapidly cool the metal poured into the.

mold, I use a permanent steel mold in place of the ordinary sand mold or cheek rammed with sand. I have obtained good results with the wall of a steel mold 4 inches thick and have obtained better results with the wall 5 inches thick, because the thicker wall provides a better heat absorbing body. The permanent steel mold in connection with the steel bottom plate not only absorbs the shrinkage which ordinarily takes place in steel castings but also reduces the temperature of the poured metal in contact with the sand below the combining temperature of the I poured metal with the material of the core.

By my method of casting it is readily seen that as fast as portions of the castings solidify, any shrinkage which may take place is immedlately fed by the incoming stream of molten metal, which, in turn, progressively solidifies until finally a solid casting is produced with practically no shrinkage taking place after the conclusion of the 'pouring of the metal. This desirable result is due to the extremely rapid cooling of the poured metal by means of the outer mold or chill composed of metal which rapidly absorbs the heat from the poured metal and conducts it away therefrom. This result is further due to the extremely slow pouring thereby reducing the. shrinkage to a minimum.

In order to explain how the combination of the molten metal with the material of the core is prevented I will state what takes place in ordinary castings which are made in a mold composed of sand altogether. The iron oxid or scale which is formed on the skin of the casting has the property of combining with silica to form a fluid slag at relatively low temperatures. Molding sand is composed largely of silica and is a. very poor conductor of heat. The portion of the sand next to the cast metal, and therefore in contact with the scale, soon absorbs heat from the cast metal and a chemical union takes place according to the equation FeO+SiO FeSiO if the temperature at which such union can take place is attained. Such chemical union results in a silicate of iron which is readily fusible at a temperature lower than 2200 F., and which has the property of dissolving further quantities of silica and iron oxid. This fusible silicate of iron becomes incorporated with the surface of the steel in castings made in the ordinary way in sand molds and causes the sand to adhere very firmly to the surface of the casting, increasing the cost of production owing to the difficulty of cleaning this off, and often seriously affecting the value of the casting. By rapidly cooling the casting in the outer metal mold or chill which is a good conductor of heat I prevent the absorption of suflicient heat by the sand next to the casting and in contact with the scale or iron oxid to permit the silica and iron oxid to attain the temperature requisite for their combination.

I have found it advantageous to pour more than one mold at a time. I found that when only one mold is poured,'it was filled too rapidly so that the heat in the poured metal was not conducted away from the sand sufficiently rapid to prevent the combinatake for each mold an equal part of a stream of metal being oured from the ladle, good results being 0 tained with the stream ofv metal 2% inches in diameter. I have found that the temperature of the metal poured into the mold to be too high for securing the best results when the mold in which the said metal is poured reaches .a red heat. This may be avoided, as is already apparent, by prolonging the pouring operation or by increasing the thickness of the mold wall, or both. The mold wall could be artificially cooled if desired to reduce the temperature thereof and, accordingly, of the molten metal in the molds.

Another object of the present invention is to provide a continuous process for the manufacture of ingot molds. By this process, I provide a metal base-plate composed-preferably of steel. This base-plate is sulficiently large to support fouremolds which are arranged symmetrically around a central runner. On this base-plate the four cores are formed substantially in the manner heretofore described. Four steel chills or molds already retaining the heat from. a previous casting operation are lowered over the said cores and in contact with the baseplate. Gas burners are lighted at the bottom of each of the central pipes in the cores and other burners are preferably employed externally of the molds or chills to maintain them at a suitabletemperature for the reception of the molten metal for the ingot molds, as cold molds are not suitable for casting. The assembled cores and molds on the base plates are then covered in a suitable manner so as to retain more or less of the heat from the said burners and to provide for heating the molds equally. As soon as the cores have been sufficiently dried, a ladle of molten steel is brought to the molds, the molds having been previously uncovered, and the metal poured into the central runner, fromwhich it radiates through runners in the base plate to the gates at the bottom of the molding spaces between the cores and the metal molds. The size of the gates and the rate of pouring the metal are so proportioned that the temperature of the poured metal in contact with each core is kept below the combining temperature of the molten metal and the core material, and so that the shrinkage, which ordinarily takes place in the interior of a-v casting after the pouring has ceased and which must be fed from sinking heads, is automatically fed or absorbed as hereinbefore described. In about'ten minutes after the pouring has ceased the center tubes in the cores are withdrawn so that the cooling ingot molds may contract without any resistance from the cores. Within a few minutes after the conclusion of the pouring, say, within twenty or thirty minutes, the molds are stripped from step in the process or operation shall not have to wait for the completion of another.

Referring to the accompanying drawings, Figure 1 shows the cores formed on a baseplate and the molds suspended over the cores preparatory to their being lowered to the base-plate with the cores within them. Fig. 2 shows at the right the cover and adjacent parts as they are during the drying of the cores and the heating of the molds, and at the left the cover removed and the molds ready to be poured from the ladle. Fig. 3shows the molds beingstripped from the ingot mold.

On the drawings, A, G, D represent the base plateson Figs. 1, 2, and 3, respectively.

pipes heat the interiors of the cores and dry them as already explained. Gas burners C,

(Fig. 2) heat the exteriors of the molds. After the burners G and C are lighted the and cores. After the cores are thoroughly dried, the cover is removed and the ladle C, containing molten steel is brought to the molds (Fig. 2) and the metal in the ladle is cover B is lowered over the assembled molds poured into the molds byway of the central runner 0. Within a few minutes after the completion of thepouring, the pipes ormandrels are removed from the cores for the purpose hereinbefore described and soon afterward the molds are stripped from the over another set of 'coreswhich have in the meantime been formed ready for drying.

The process just briefly outlined is preferably made continuous. Cores are being made at one or more places while other cores are drying at one or more other places, ingot molds are being cast and stripped at one or more other places. If preferred the ingot molds, as shown. on Fig. 3, and placed base plates with the cores thereon can be moved to a special. drying position or to a pit, but it is preferredthat the drying be filling of the mold and the setting of the done without moving the base-plate and cores, as the cores may become damaged by the moving. It is, however, to be understood that these several operations, considered separately or taken in groups of two or more, have advantages over the operations of the usual practice. The employment of the preliminary mold and of the final, or ingot-mold, cast within the preliminary mold, and the return of the preliminary mold to the core of another final mold after an ingot-mold has been cast therein are novel and reduce the cost of manufacture materially.

By the method herein described, the heat absorbing capacity of the outer metal mold is so proportioned to the rate and volume of flow of the metal into the mold that the poured metal to a pasty or non-shrinking condition take place simultaneously, whereby the mold is filled full, internal shrinkage is obviated, and sink-heads or risers are dispensed with.

My invention also includes the making ofingots. Heretofore ingots have been made by first casting a cast iron ingot-mold between a silicious core and a siliciousouter mold wall. 'Such ingot molds have, as above stated, a rough uneven interior which must be smoothed at a considerable cost; they have on their tops large sink-heads which require expensive machinery and a large amount of labor for their removal; and they become Warped after a few ingots have been cast therein. Furthermore, it has been the opinion generally of foundrymen that it is not feasible to provide cast steel molds for ingots. By my invention ingots can be successfully made at a minimum cost if the molds therefor are first made as herein specified.

The interior surface of steel ingot molds may be conserved ifthe carbon, or other alloymg content, as phosphorus, sulfur, etc., in the ingot-mold be not more than 2 per cent. above the content of the, like alloying In case the'alloying content in the ingot. content in the ingot-mold is much above that in the ingot, the ingot in the fluid state immigrates or infuses itself into the wall of the ingot-mold, causing parts of the. said wall'to slough 0E and become suspended in the ingot, causing cavities in the mold wall .and hard spots in the ingot.

This application is in part for the subject matter of my applications, Serial Numbers 720,174 and 720,175, filed September 13, 1912, and Serial Number 722,927, filed September 28,1912, to which reference is made for further details of construction and practice.

I claim 1. The method of surfacing the molding surface of a cast steel mold which consists in casting said molding surface in contact with a silicious material while maintaining the contact below the temperature of combination of said silicious material and steel.

2. The method of surfacing the molding surface of a. cast steel mold which 'consists in casting said molding surface in contact with a silicious material while maintaining the contact below the temperature of combination of said silicious material and steel by proportioning the rate of flow to the loss of heat. p

3. The method of making an ingot mold which consists in pouring molten steel into a molding space bounded externally by a metal mold and internally by a core composed of pure silica, about 95 per cent, and cl 4. The method of making an ingot mold which consists in pouring molten steel into a molding space bounded externally by a metal mold and internally .by a core composed of pure silica, about 95 per cent, and Welsh Mountain clay.

5. The method of preparing cores and molds for casting steel ingot molds which consists in forming hollow cores containing silicious material, surrounding the cores with metal molds, drying the cores from inside outwardly, .and uniformly heating the molds.

Signed at Pittsburgh, Pa, this 3rd day of 1 December, A. D. 1912.

CHARLES G. ROBINSON. Witnesses:

ALICE E. DUFF, F. N. BALBER. 

